Rotomoulding is used for the manufacture of simple to complex, hollow plastic products. It can be used to mould a variety of materials such as polyethylene, polypropylene, polycarbonate polyamide, or polyvinyl chloride (PVC). Linear low density polyethylene is preferably used as disclosed for example in “Some new results on rotational moulding of metallocene polyethylenes” by D. Annechini, E. Takacs and J. Vlachopoulos in ANTEC, vol. 1, 2001.
Fluoropolymers, for example those based on vinylidene fluoride CF2═CH2 (VDF) such as PVDF (polyvinylidene fluoride), are known to offer excellent mechanical stability properties, very great chemical inertness and good ageing resistance. These qualities are exploited for various fields of application. For example, mention may be made of the manufacture of extruded or injection-moulded parts for the chemical engineering industry or for microelectronics, the use in the form of impermeable ducts for transporting gases or hydrocarbons, the production of films or coatings for protection in the architectural field, and the production of protective elements for electrical engineering uses. However, this chemical inertness of fluoropolymers means that it is difficult to bond them or combine them with other materials.
Polyethylene represents more than 80 percent of the polymers used in the rotomoulding market. This is due to the outstanding resistance of polyethylene to thermal degradation during processing, to its easy grinding, good flowability, and low temperature impact properties.
Multi-layer articles of polyolefins with fluoropolymers formed by the rotomolding process are described in European patent application EP 02079876.5.
Plastoelastomeric compositions such as described in U.S. Pat. No. 5,457,159 can also be used in rotomoulding, but they require complex processing steps of mixing and vulcanisation.
U.S. Pat. No. 6,124,400 discloses the use for rotomoulding of polymer alloys containing semi-crystalline polyolefin sequences with chains of different controlled microstructure prepared in a “one-pot” polymerisation process from a single monomer. The polymerization of these polymer alloys requires a complex catalyst system comprising organometallic catalyst precursors, cationic forming cocatalysts and cross-over agents.
There is a need for multi-layer rotomolded article having a fluoropolymer layer, with improved bonding between the fluoropolymer layer and other layers of the article.
Surprising it has been found that functionalised fluoropolymers combined with functionalised non-fluoropolymers in a rotomolding process achieve excellent bonding between the layers.